Linoleic acid and alpha-linolenic acid are two fatty acids that cannot be synthesized by humans, thus these two fatty acids are considered to be Essential Fatty Acids (EFA's) necessary in human nutrition. Linoleic acid and alpha-linolenic acid form polyunsaturated fatty acids of the omega-6 series and omega-3 series, respectively, through enzymatic desaturation and elongation principally by the liver. While man and other mammals can desaturate or elongate the fatty acid chains they cannot interconvert the fatty acids from one family to another (e.g. Omega-6 to Omega-3). Accordingly, both linoleic and alpha-linoleic fatty acids have been included in all total Enteral and Parenteral Nutritional products to date.
In the United States it is recommended that 3% of the total calories in the diet be from linoleic acid. Linoleic acid intake at levels from 1% to 2% of total dietary calories is believed to be sufficient to prevent both biochemical and clinical evidence of deficiency in several animal species and humans. The Academy of Pediatrics has recommended that infant formulas provide at least 2.7% of energy as linoleic acid (Recommended Dietary Allowances 10th Edition, 1989, Author: Subcommittee on the Tenth Edition of the RDA's Food and Nutrition Board Commission on Life Sciences; Publisher: National Academy Press Washington, D.C.)
Essential fatty acids are known to play a part in many metabolic processes, and there is evidence to suggest that low levels of essential fatty acids, or the wrong balance of types among the essential fatty acids, may be a factor in a number of illnesses including, for example, metabolic syndrome, heart disease, fatty liver disease, obesity and diabetes.
Accordingly, it is important to have an improved understanding of the essential fatty acids and their effects so that better nutritional programs can be designed.
Parenteral nutrition (PN) is a life-saving therapy for patients unable to absorb enteral nutrients secondary to insufficient intestinal length or function. Before the development of PN, patients with insufficient gastrointestinal absorptive function commonly died of starvation and subsequent complications of malnutrition1. Today, more than 30,000 patients in the US are permanently dependent on PN for survival. Long-term use of PN, however, is associated with many complications, including blood stream infections, metabolic abnormalities and organ dysfunction2. The most serious complication in children continues to be PN-associated liver disease (PNALD), whose etiology has been demonstrated by our team to be at least in part due to the lipid emulsion component3,4. The most effective treatment for PNALD is increasing enteral energy intake while reducing PN, but this process is often impossible when intestinal function is poor5,6. In some cases of liver dysfunction in the setting of intestinal failure, liver-small intestine transplantation remains the only treatment option. Infants with PNALD have a mortality rate approaching 100% within a year of diagnosis if they are unable to be weaned off PN or fail to receive a liver/small bowel transplant'. Recent evidence suggests that PNALD may be in part due to the lipid component that is rich in soy oils containing large quantities of pro-inflammatory omega-6 fatty acids and hepatotoxic phytosterols 8,9. A fish oil-based lipid emulsion has been shown to be hepatoprotective in mice and efficacious in the treatment of PNALD in children3, 4, 10, 11 